Studies of the human testis. XIII. Properties of nicotinamide adenine dinucleotide (reduced form)-linked 17 alpha-hydroxylation.

A NADH-linked 17 alpha-hydroxylation of progesterone was examined using the washed microsome fraction prepared from human testes. The addition of NADP revealed no enhancement of 17 alpha-hydroxylation, indicating no transhydrogenation from NADH to NADP in the microsome fraction. The results further substantiate the presence of NADH-linked activity of 17 alpha-hydroxylation in addition to NADPH-linked activity. The Km of 17 alpha-hydroxylase for NADH was calculated as 4.3 x 10(-5) M at pH 7.4 and 37 C. The optimal pH of 17 alpha-hydroxylase was 7.7 in the presence of NADH and 7.9 in the presence of NADPH. An additive increase in the amount of product 17 alpha-hydroxyprogesterone was observed by adding NADH to the incubation medium containing an excess amount of NADPH. The data suggest that there are two distinct active sites for 17 alpha-hydroxylation. Furthermore, the inhibition of NADH-linked 17 alpha-hydroxylation by carbon monoxide indicates the involvement of cytochrome P450 in the electron transport system for the NADH-linked 17 alpha-hydroxylation.